High Pitch Ringing Noise

I have a 2001 330ci that I just recently purchased and am having the weirdest issue. It only happens when im going between 80-85 MPH and giving the throttle about 15%-20% power, but when I do a high pitch ringing noise comes from the back of the car. I cant hear it with any music on but and it only comes on during those certain conditions but has anyone experienced anything similar or have any advice for me?



Thanks in advance, any help is much appreciated.